HOUSTON — The U.S. shale gas revolution will go global over the next two decades, with production expanding rapidly in China, Argentina and Canada as natural gas eats into oil’s share of global energy demand to become the fastest-growing fossil fuel, BP says.

In its annual Energy Outlook released Wednesday, BP projected shale gas production around the world will grow 5.6 percent a year, and by 2035, half the growth in shale energy will come from outside the United States. BP expects China to overtake the United States as the biggest factor behind shale gas production growth by 2035, after U.S. shale resources reach their peak.

Late last year, BP struck two multibillion-dollar deals with China to help cultivate its vast shale natural gas resources as part of China’s efforts to reduce air pollution from the massive amount of coal it burns for power. More broadly, the British oil giant expects to pump more natural gas than oil in just a few years.

“Our portfolio is already around half natural gas and is heading toward more gas with some very big projects on course, on budget,” BP CEO Bob Dudley said during the webcast. “We could be 60 percent gas by the end of this decade.”

BP expects to extract natural gas from its project in the Nile Delta in Egypt, in the Khazzan field in Oman and its giant Shah Deniz 2 project in Azerbaijan, and it is building major gas pipelines in Europe.

In the United States, shale drillers have learned how to pump more and more oil and gas and have “unlocked vast resources,” Dale said.

“We’ve been repeatedly surprised by the strength of U.S. shale,” he said.

BP has revised its projections for shale oil and gas higher each year since 2013. Just three years ago, BP believed U.S. tight oil would peter out at less than 4 million barrels a day by the end of the decade. Now, domestic tight oil is expected to rise to about double that by 2035.

U.S. shale oil has declined by half a million barrels a day since April last year and will likely keep falling amid low crude prices and high natural decline rates.

“But as the oil market gradually rebalances, and prices eventually firm, we expect U.S. tight oil to increase by almost 4 million barrels a day … and account for almost 20 percent of total U.S. production (over the years),” Dale said.

Globally, tight oil production could rise to 10 million barrels a day, as the world’s appetite for crude increases by 20 million barrels a day by 2035. That’s still just 10 percent of the broader oil market, and the growth is set to slow.

North America’s daily tight oil output could sink from 4.5 million barrels over the past decade to 2.5 million from now until 2025, and then lower to 1 million in the following 10 years.

“The role of shale gas is more pronounced with its share in global gas production increasing from a little over 10 percent today to a little over 25 percent by 2035,” Dale said.

U.S. shale gas will keep growing even after tight oil production declines set in over the next decade. BP projecting domestic shale gas output will increase 4 percent a year to reach about 80 billion cubic feet a day over the next 20 years.

Chinese shale gas production will boost that greatly, but its economic growth may weigh on energy markets. China’s economy, Dale said, is shifting away from growth in energy-intensive industrial sectors and toward consumer-oriented service sectors, rebalancing after a decade of surging economic growth.

BP expects China’s energy demand to grow on average less than 2 percent a year over the next 20 years, about a quarter of its rate for the last 15 years.

“The most marked changed from the past is in China’s coal consumption, which after years of strong growth as it fueled China’s rapid industrialization, barely grows over the outlook and is declining toward the end,” Dale said. “So, big shifts in the world’s largest energy market over the next 20 years.”